When writers decide to skip the pause comma after introductory phrases, it can cause some confusion about when a comma is truly needed. For this reason, we thought it might be helpful to quickly review the Chicago Manual of Style rules on commas with dependent clauses.
Essentially, when a sentence begins with if, because, until, whether, or when, that's a signal to always use a comma after that introductory phrase.
So it’s OK to skip the comma when a sentence opens with a regular old prepositional phrase, such as cases like these:
In the summertime we like to swim.
Of course we’ll join you for dinner. (Sidebar: adding a comma here would change the meaning slightly.)
By tomorrow we should be finished with your lessons.
But when that intro clause is dependent and causes a condition, the comma is necessary to signal that. (Plus, the comma helps the reader to know where to pause, which makes long conditional sentences easier to parse.)
If I get invited to the party, I’ll go.
Because you were polite, I’ll consider your request.
Until I hear from him, I won’t take any action.
Whether you meant to or not, you really cheered her up.
When he calls back, tell him I’m on my way.
On the other hand, when some of these same phrases are used at the end of the sentence rather than at the beginning, no comma is necessary because the phrase is restrictive (meaning it's essential to understanding the full meaning of the sentence):
I'll go if I get invited to the party.
I'll consider your request because you were polite.
I won't take any action until I hear from him.
In these three cases, the first statement of the sentence is not true unless the second part is also true. (You'll also notice that they're much easier to read, without the need to "pause" with a comma.)
We hope you've found this explanation helpful. But if the issue still seems confusing, feel free to reach out to us at firstname.lastname@example.org. (OR: Feel free to reach out to us if the issue still seems confuing. ;-} )
Editing tip: A quick way to make sure you’ve applied the first rule globally is to use the Advanced Search feature in Microsoft Word to search for each intro word we listed above; be sure to add a space before it, capitalize it, and set the search to Match Case only. This will allow you to scan only the sentences that begin with these subordinating conjunctions.
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